Indoor air quality: reconciling air renewal and energy performance

The harmful effects of indoor air pollution on the health of occupants no longer need to be demonstrated. Air renewal and ventilation are therefore fundamental in order to meet the comfort and health requirements of the occupants.

In order to achieve the ambitious objectives in terms of energy saving and the fight against global warming, the major challenge is to maintain a quality indoor environment (thermal comfort, indoor air quality - IAQ, acoustic comfort) while reducing the energy consumption of the building.

The need for good air quality and air renewal

We now spend 90% of our time in closed environments (housing, businesses, nurseries, schools, transport, etc.) where indoor air can reveal a level of pollution up to ten times higher than outdoor air. The harmful effects of indoor air pollution on the health of occupants no longer need to be demonstrated: sick building syndrome, asthma, cocktail effects, effects on work performance. The cost of the socio-economic effects of poor indoor air quality in France is currently estimated at 19 billion euros per year for just 6 pollutants (see sources 1). A real societal issue because linked to public health, improving indoor air quality (IAQ) requires efficient ventilation with systems that must meet a dual challenge: that of ensuring air renewal sufficient while minimizing the energy impact.

To do this, it is necessary to work on reducing direct energy consumption linked to the consumption of auxiliaries and indirect energy consumption linked to air renewal (heating and cooling requirements).

There are three levers of action:

• Acting on the electricity consumption of the fans with the use of electronically commutated (EC) motors, whose regulated speed makes it possible to reduce its consumption, and the optimization of the performance of the fans.
• Optimize air renewal. This is done in two main ways: via the concept of sweeping (supply of air in the living rooms and extraction in the polluted premises), very present in France, and via the modulation of the flows in housing and in the tertiary sector. This modulation makes it possible to adapt the airflows to the real need.
• Recover energy from the extract air by using heat exchangers (plate or wheel) between the extract air and the fresh air and by using the extract air as a source for the multifunction devices (heat pump or thermodynamic water heaters).

What are the challenges of air renewal?

The first challenge is to meet the health and comfort requirements of the occupants by bringing in fresh air from outside, evacuating stale air and diluting pollutants. The second challenge is to contribute to the preservation of the building by avoiding the risk of condensation and therefore the development of mould.

Air renewal can be done in three ways:

• air infiltration resulting from the permeability of the building. Uncontrollable, they are today incompatible with the airtightness requirements of buildings.
• the opening of the windows which makes it possible to bring a high air flow from time to time, in particular after a peak of activity. However, this method remains closely linked to the user and to external constraints (climate, acoustics, burglary, etc.). It is therefore not possible to rely on this solution alone to ensure good IAQ.
• a ventilation system to ensure the renewal of air in the buildings. Thanks to a localized air supply, control of flow rates and complete treatment of the building, this solution is the most convincing and the most efficient. These ventilation systems must meet requirements relating in particular to energy performance, fire safety, acoustic comfort and sustainable development. Where applicable, they must also be compatible with the correct operation of combustion appliances, in order to avoid draft reversals.

There are several action levers to improve the efficiency of the ventilation system to maintain good IAQ while reducing energy consumption.

Clearing the air, a well-known IAQ improvement lever

A first solution consists in purifying the air, either with different types of filter media (fiberglass, fibers, filters with electret treatment, etc.), or by other technologies (ionization, photocatalysis, etc.). This will thus make it possible to reduce the level of particles in the air coming from outside, pollens, micro-organisms, germs or other bacteria penetrating into the premises (purification integrated into the ventilation) or present in the air. environment (autonomous air purifier).

However, unlike a ventilation system which extracts all pollutants from the air without distinction, air purification only treats a target family of pollutants (chemical, bacterial or particulate). It is therefore necessary to combine several purification techniques if the whole range of pollutants is to be treated. In addition, some pollutants are not treated by purification (CO2 for example). So purification alone cannot be the solution. It must be associated with efficient ventilation.

Intelligent ventilation, a lever for the future

The definition given by the AIVC (sources 2) for smart building ventilation is as follows: "Smart ventilation is a process of continuous adjustment of the ventilation system over time, and possibly according to location, to provide the desired indoor air quality (IAQ) while minimizing energy consumption and energy bill, as well as other non-IAQ related drawbacks, such as thermal discomfort or noise”.

An intelligent ventilation system reacts in particular to the presence of occupants, to IAQ criteria, to the needs of the electrical network, to the temperature or relative humidity outside, to indoor pollution or to the operation of other systems.

According to a CETIAT study on tertiary buildings (sources 3), the average occupancy rate of an office is 40% and 10% for a meeting room, which tends to prove the interest of using to the modulation of flows. This modulation will be linked to humidity sensors (which we know above all in the residential sector with humidity sensitive systems), presence detection (in toilets and in offices in the tertiary sector), optical counting and CO2 sensors. The flow rate modulation can be done either by zone, at the level of the terminals or a complete branch of the aeraulic network, or on the complete scale of the building by acting directly on the fan.

In order to verify and enhance the efficiency of flow modulation systems, various certifications exist both at French (NF, QB) and European (Eurovent, Passivhaus) levels. The performance of the products and the values ​​announced by the manufacturers are thus controlled by an independent third-party body.

Ventilation equipment, once installed, must be checked. In new residential buildings, the RE2020 environmental regulation has included in its texts the obligation to have ventilation systems checked by an independent professional. A compliance indicator will be included in the RE2020 certificate, the user will therefore be able to have precise information on the compliance of his installation.

IAQ is everyone's business during the construction of a building: from programming to the operating phase and operation, all trades related to the construction of buildings are involved in this indoor air quality. . It has been perceived for some time now that the impact of buildings on the health and well-being of occupants is taking an increasingly important place in public opinion, in the same way as energy performance.

1: ANSES-CSTB report, April 2014 - https://www.oqai.fr/fr/campagnes/cout-socio-economique-de-la-pollution-de-l-air-interieur - Pollutants studied: benzene, radon, trichlorethylene, CO, particles, environmental tobacco smoke

2: F. DURIER, R. CARRIÉ and M. SHERMAN. "What is smart ventilation?". Breakdown Information Paper No. 38, May 2018 - https://www.aivc.org/sites/default/files/VIP38_french.pdf

3: Technical Note CETIAT NTV 2000/071, "Flow modulation", 176 pages, September 2000

Tribune by Benoît Golaz, Aeraulic Ventilation Systems project manager at CETIAT (LinkedIn)